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re-frame-trace

re-frame-trace let's you look at the inner workings of a running re-frame application. It presents as a programmer's dashboard, delivering curated insight and illumination. Because you know more, your capacity to debug will increase.

It Is Epoch Oriented

re-frame applications are computationally regular. First an event happens, and then boom, boom, boom go a series of known computational steps (aka dominoes), in a known order. When this chain reaction completes, a re-frame app enters a quiescent state waiting for another event to kick off the next iteration of the same process.

Each re-frame event and its consequent computation forms a bounded "epoch" which can be inspected, analysed and understood independently of other epochs. This tool is epoch-oriented - it shows you one at a time.

And, yes, it has "time travel debugger" capabilities - you can go backwards and forwards through epochs - but that's really not the most interesting or powerful aspect of what re-frame-trace delivers.

It Is About Trace Data

As it runs, re-frame logs "trace" as data (not strings). This data trace provides an x-ray of your app's functioning.

re-frame-trace is essentially a consumer, processor and displayer of this x-ray trace data.

It Is About The Data Flow

While re-frame is a functional framework, it is strongly defined by its "data oriented" design. re-frame "flows" data, in a loop, through the functions you provide. To understand what is happening in a re-frame app, you must understand what data is "happening".

It is Just About Data

So, data is at the core of re-frame-trace in both of the ways just described, and that should not be the slightest bit surprising.

Each time you put a println into your program, you are printing out what? And why? Data is the fuel of your debugging investigation.

Have you seen LightTable? It was attractive because it co-renders data and code. The data presented is the "paper trail" by which you can percieve the dynamics of the code.

It Is A Data Dashboard

Observing raw data is certaintly interesting, but it isn't enough. Data is the substrate we want to leverage. Apart from anything else, there's often too much data - you can drown in the detail.

So, re-frame-trace tries to be a "dashboard" which curates this "raw data" into "information" through various kinds of analysis and "roll ups". It should deliver insight "at a glance", while still allowing you to drill down into the detail.

Which Is Helpful How?

Four ways:

It helps you to learn re-frame. Simply looking at the "raw traces" provides insight into how it operates. Even experienced re-framians, er, like me, have learned a lot.
It helps you to explore and learn an unfamiliar re-frame codebase. When I click, over here, on this "X" button, it shows me what event is dispatch-ed and in what namespace the associated event handler is registered. And, "oh look, that's interesting - four subscriptions recalculated". Etc.
It helps you with debugging. You see an x-ray of your app's functioning. In particular, it will assist you to write and debug event handlers, which is useful because they hold most of the logic in your re-frame apps.
It helps you to find performance problems and/or detect where there is unnecessary computation occurring.

Deeper knowledge is the goal. Easier debugging is the symptom.

Temporary Warning

Some of the claims above are aspirational. re-frame-trace remains a WIP experiment. But we're getting there.

The Name

We debated internally about the name re-frame-trace. We knew that -trace was okay, but anemic because it talked about low level function, not higher level benefit. I wanted to call it vox-datum (voice of the data) but that was cruelly rejected, for reasons I don't care to remember. The pain. I mean, who the hell doesn't like a Latin name?? Philistines. Anyway, "insight" and "illumination" are the benefits, but they made the name too long. Naming things - its a nightmare! As is inertia. So, -trace it remains.

A Visual Sampler

Slightly out of date, but indicative ...

Installation

If you are using leiningen, modify project.clj in the following ways. When puzzling over the various possible leiningen configurations, it's often helpful to look at a sample project.clj.

Update your re-frame dependency to at least 0.10.4 - [re-frame "0.10.4"].
Add re-frame-trace as a dev dependency by placing [day8.re-frame/trace "VERSION"] within :profiles :dev :dependencies. For example:
```
:profiles
   {:dev
      {:dependencies [[some-other-package  "0.0.0"]
                      [day8.re-frame/trace "0.0.0 (see version above)"]] }}
```
If your project uses React 16 and Reagent 0.8.0-alpha2 (or higher) then you will need to add the qualifier -react16 to the version, e.g. [day8.re-frame/trace "0.0.0-react16"].

Locate the :compiler map under :dev and add:

:closure-defines {"re_frame.trace.trace_enabled_QMARK_" true}
:preloads [day8.re-frame.trace.preload]

For example:

{:builds
   [{:id           "dev"
     :source-paths ["src" "dev"]
     :compiler     {...
                    :closure-defines      {"re_frame.trace.trace_enabled_QMARK_" true}
                    :preloads             [day8.re-frame.trace.preload]
                    }}]}

cljs-devtools is not required to use re-frame-trace, but it is highly recommended.

Usage

Make sure you have followed all of the installation instructions above.
Start up your application.
Once it is loaded, focus the document window and press ctrl-h to slide open the trace panel and enable tracing.
When the panel is closed, tracing is disabled.

Use Cases

app-db

Inspect a portion of app-db's state with the path inspector, allowing you to focus on just the parts you care about.
Reset app-db to before an event was run to run it again, instead of resetting the whole application
Toggle app-db before and after states for running an event, to inspect UI changes.

Timing

Answer the question "Why is my app slow when it runs this event?"
See whether time is spent in processing an event, or rendering the changes

Troubleshooting

Try a lein clean
Make sure you have followed all the installation steps.

If re-frame-trace throws an exception on startup

Reset the settings to factory defaults in the settings panel
If you can't load the settings panel, run day8.re_frame.trace.factory_reset_BANG_() in the JavaScript console.
If neither of those work, remove all of the keys with the prefix day8.re-frame.trace from your browser's Local Storage.

How does it work?

re-frame is instrumented - all important activity generates trace data.

re-frame-trace consumes this trace data and renders useful visualisations of the re-frame process. Currently, re-frame's tracing capabilities are in alpha and are subject to change at any time. We're testing the utility of the the trace by building an app on top.

By default, re-frame tracing is "compiled out", so it won't impose a performance cost in production. The trade-off here is that you need to explicitly enable it in development.

The preloads option (:preloads [day8.re-frame.trace.preload]) has to be set in order to automatically monkeypatch Reagent to add appropriate lifecycle hooks. Yes this is gross, and yes we will make a PR to reagent to add proper hooks, once we know exactly what we need. The preload namespace also injects a div containing the devtools panel into the DOM.

Developing/Contributing

If you want to work on re-frame-trace, see DEVELOPERS.md.

Citations

open by Bluetip Design from the Noun Project
reload by Adnen Kadri from the Noun Project
Camera by Christian Shannon from the Noun Project
Delete by logan from the Noun Project
Settings by arjuazka from the Noun Project
Wrench by Aleksandr Vector from the Noun Project
pause by Bhuvan from the Noun Project
play by Bhuvan from the Noun Project
Log Out by Arthur Shlain from the Noun Project

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